The present invention relates to a communication system, and more particularly, to a communication system for determining at least a target impairment calibration parameter for calibrating impairment in a transmission signal according to a single tone testing signal having a specific frequency or according to combinations of a DC value and the single tone signal.
In general, for a communication system (for example, a transceiver) to generate a transmitting signal, two factors, including carrier leakage and IQ imbalance, are considered when considering the performance of the communication system, where the carrier leakage and the IQ imbalance are usually called impairments for the communication system. In an ideal situation, the impairments are not introduced into the communication system; in reality, however, they often occur, resulting largely from non-ideal characteristics of electronic components or mismatches between electronic components or circuits. For example, when a local oscillator re-radiation from the antenna is produced, the DC offset introduced by carrier leakage is not desirable when performing an up-converting operation to generate the transmitting signal because the DC offset is also up-converted.
Additionally, the IQ imbalance is not desirable for the transmitting module's up-converting operation. The IQ imbalance includes gain imbalance and phase imbalance, wherein gain imbalance means a mismatch between gains of signals in the in-phase transmitting path and the quadrature-phase transmitting path, and phase imbalance means a mismatch between phases of carrier signals in the in-phase transmitting path and the quadrature-phase transmitting path. Specifically, because gains of signals in the in-phase transmitting path and the quadrature-phase transmitting path are not guaranteed to be identical and phases of carrier signals in the in-phase transmitting path and the quadrature-phase transmitting path are not guaranteed to be orthogonal, gain imbalance and phase imbalance must be considered.
Therefore, decreasing the influence caused by the above-mentioned impairments is very important when the transmitting module performs the up-converting operation. Usually, different calibration parameters are utilized for calibrating the transmitting paths to decrease the influence caused by the impairments, i.e. the carrier leakage and the IQ imbalance, such that the performance of the communication system is improved. Therefore, a novel and improved scheme for determining these calibration parameters efficiently is needed.